You may have noticed an asymmetry between the vegetation along the creek and the vegetation of the slopes immediately adjacent. Well spotted! This is the paradox of the lush Sonoran Riparian ecosystem embedded within a surrounding Sonoran Desert landscape. And, as you may also have guessed, it's all about the water.

Permanent surface water here in Aravaipa Creek and, in any stream or river anywhere, results when the surface of the land intersects the surface of the groundwater horizon. This rule applies especially clearly to streams in the desert. Here, deciduous forests of cottonwood, willow, ash, walnut, sycamore, alder, and other species of Temperate origin are found, literally within arm's reach, of subtropical Sonoran Desertscrub, dominated by succulents, legumes, and numerous drought-tolerant shrubs and perennial herbs which evolved in the Neotropics.